Brake Rotor With Working Surface Inserts

ABSTRACT

A brake rotor assembly can include a structural part having a receiving surface and at least one friction surface parts having a contact surface. The friction surface part can be fixably attached to the receiving surface of the structural part such that the contact surface faces away from the receiving surface of the structural surface to form at least part of an annular braking surface arranged concentrically around an axis of rotation of the structural part.

CROSS-REFERENCE TO RELATED APPLICATION

The current application claims priority to U.S. Provisional ApplicationSer. No. 62/000,461 filed May 19, 2014, the disclosure of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The subject matter described herein relates generally to brakingsystems.

BACKGROUND

A braking system generally includes two surfaces that are urged intocontact with one another when the braking system is actuated, forexample when an operator of a vehicle, or alternatively one or moreautomated or semi-automated safety systems of the vehicle, operates acontrol to applying braking force to slow rotation of an axle of avehicle and to thereby slow or stop the vehicle. A first surface of thetwo surfaces can be part of a rotor assembly, which is generally mountedin association with (e.g. rotationally fixed to) an axle and one or morewheels of the vehicle, and which rotates at a same rotational velocityas the one or more wheels. A second surface of the two surfaces can bepart of a pressure applicator assembly, which can be mounted such thatthe pressure applicator assembly does not rotate with the one or morewheels.

SUMMARY

In one aspect, a brake rotor assembly includes a structural part, whichcan have having a receiving surface aligned perpendicularly to an axisof rotation of the structural part, and a friction surface part having acontact surface. The friction surface part is fixably attached to thereceiving surface of the structural part such that the contact surfacefaces away from the receiving surface of the structural surface to format least part of an annular braking surface arranged concentricallyaround the axis of rotation.

In an interrelated aspect, a braking system includes the aforementionedbrake rotor assembly, a brake pad that includes a friction material, andan apparatus for urging the friction material of the brake pad againstthe annular braking surface to slow rotation of the brake rotor assemblyand a vehicle axle to which the brake rotor assembly is rotationallyfixed.

In yet another interrelated aspect, a method for assembling a brakerotor assembly includes positioning a friction surface part having acontact surface on a receiving surface of a structural part and fixablyattaching the friction surface part to the receiving surface of thestructural part such that the contact surface faces away from thereceiving surface of the structural part to form at least part of anannular braking surface arranged concentrically around an axis ofrotation of the structural part.

In some variations one or more of the following features can optionallybe included in any feasible combination. The friction material caninclude at least one of stainless steel, cast iron, a ceramic, and acomposite, and the friction surface part can include a brake padmaterial. The friction material of the brake pad can include at leastone of stainless steel, cast iron, a ceramic, a composite, and a brakepad material. The friction material of the brake pad can include a wearand corrosion resistant coating. The friction surface part can include asame material as the friction material of the brake pad. The frictionmaterial of the brake pad can include one or more levels of surfacetopography

The friction surface part can include a plurality of friction surfaceparts arranged on the receiving surface to form the at least part of theannular braking surface. The friction surface part can include at leastone of stainless steel, cast iron, a ceramic, a composite, and a brakepad material.

The contact surface of the friction surface part can include a wear andcorrosion resistant coating. The contact surface of the friction surfacepart can alternatively or additionally include one or more levels ofsurface topography. The one or more levels of surface topography caninclude a first level that includes island formations separated bychannels. The one or more levels of surface topography can furtherinclude a second level comprising raised peaks with spaced valleysbetween the peaks. The second level of surface topography can assist inretaining the transferred film or layer of brake pad material on thecontact surface. The transferred film or layer of brake pad material canenhance braking by participating in adhesive friction with a brake pad.

The structural part can be formed of at least one bulk material selectedfrom a ceramic, a metal matrix, a composite material, cast iron, andcarbon fiber. The structural part can include a physical structure toenhance cooling, and this physical structure can include a vane and/or achannel. The brake rotor assembly can include an attachment feature forfixably attaching the friction surface part to the receiving surface,and this attachment feature can include at least one of a screw, a bolt,a connecting pin, an adhesive, a weld, a braze, a retaining ridge and,an at least partially recessed or indented area on the receiving surfaceinto which at least part of the friction surface part is seated.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims. The claims that follow this disclosure are intended to definethe scope of the protected subject matter.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, show certain aspects of the subject matterdisclosed herein and, together with the description, help explain someof the principles associated with the disclosed implementations. In thedrawings,

FIG. 1 shows a diagram illustrating features of a braking system;

FIG. 2 shows a diagram illustrating features of a brake rotor assemblyconsistent with implementations of the current subject matter;

FIG. 3 shows a diagram illustrating features of another brake rotorassembly consistent with implementations of the current subject matter;

FIG. 4 shows a diagram illustrating features of another brake rotorassembly consistent with implementations of the current subject matter;

FIG. 5 shows a diagram illustrating features of the brake rotor assemblyof FIG. 4;

FIG. 6A, FIG. 6B, and FIG. 6C show diagrams illustrating features ofanother brake rotor assembly consistent with implementations of thecurrent subject matter;

FIG. 7 shows a diagram illustrating a cross-sectional, magnified view ofa friction surface part having two scales of surface topography;

FIG. 8A and FIG. 8B show diagrams illustrating cross-sectional,magnified views of a brake rotor coated in a manner consistent with oneor more implementations of the current subject matter, with FIG. 8Ashowing discrete layers and FIG. 8B showing at least partial integrationof the components of separate layers to form a combined layer; and

FIG. 9 shows a process flow chart illustrating features of a methodconsistent with implementations of the current subject matter.

When practical, similar reference numbers denote similar structures,features, or elements.

DETAILED DESCRIPTION

A conventional example of a braking system 100, as illustrated in FIG.1, includes a brake rotor 102 having friction surfaces 104 machined orotherwise formed onto a substrate material and a brake pad 106positioned on a caliper or other apparatus (not shown) configured tourge the brake pad 106 against one of the friction surfaces 104. A brakepad 106 in such a braking system 100 typically includes a frictionmaterial 110 designed to participate in an abrasive friction interactionwith a friction surface 104 of the brake rotor 102 as the brake pad 106is urged against the brake rotor 102 to slow rotation of the brake rotor102 and the associated one or more wheels (not shown) about an axis ofrotation 112. The friction material 110 is typically designed to wearaway during use of the braking system 100. The abrasive frictioninteraction of the friction material 110 with the friction surface 104also typically causes wear to the friction surface such that the brakerotor 102 requires re-machining or replacement during at least someinstances of servicing or maintenance of the braking system 100.

An approach consistent with the current subject matter can include useof a modular surface on the brake rotor assembly, for example a brakerotor assembly 200 as illustrated in FIG. 2. The term modular is usedherein to refer to one or more pieces or parts of the brake rotorassembly that are not integral to the bulk structure of the brake rotorassembly. In other words, the brake rotor assembly 200 can include atleast two parts—a structural part 202 and one or more friction surfaceparts 204—that are joined together. The brake rotor assembly 200 shownin FIG. 2 includes a structural part 202 and two friction surface parts204, each of which is joined to the structural part 202 on one of twoopposed receiving surfaces 206 of the structural part 202 such that a(outer) contact surface 210 of each friction surface part 204 faces awayfrom the structural part 202 to provide a comparable function to amachined or otherwise formed friction surface 104 on a conventionalbrake rotor 102. The contact surface 210 of a friction surface part 204forms at least part of an annular braking surface arrangedconcentrically around the axis of rotation 112. In the example of FIG.2, each friction surface part forms an entirety of the annular brakingsurface. However, this need no be the case. Also as shown in FIG. 2, thestructural part 202 can optionally include vanes, channels, or otherphysical structures, for example to provide or enhance cooling of thebrake rotor assembly 200, etc.

A brake rotor assembly consistent with implementations of the currentsubject matter can be manufactured in multiple parts, which can beassembled prior to use in braking a vehicle. As illustrated in the brakerotor assembly 300 shown in FIG. 3, multiple friction surface parts 204can form either or both of two opposed friction surfaces of the brakerotor assembly 300 upon being fixably attached to one or more matingportions, for example a receiving surface 206, of a structural part 202.Fixable attachment of a friction surface part 204 to the structural part202 can be accomplished using one or more approaches. As non-limitingexamples, a friction surface part 204 can be fixably attached to astructural part 202 using one or more attachment features, such as forexample screws or bolts 302, connecting pins 304, an adhesive, weldingor brazing, one or more at least partially recessed or indented areas306 on a receiving surface 206 of the structural part 202 into which atleast part of the friction surface part 202 can be seated, or the like.The multiple friction surface parts 204 forming a friction surface ofthe brake rotor assembly 300 can optionally have a repeatable andinterchangeable shape, which can facilitate mass production of suchfriction surface parts 204. Alternatively, one or more of the multiplefriction surface parts 204 that form a friction surface of a brake rotorassembly 300 can have different shapes.

FIG. 4 shows an expanded view of another example of a brake rotorassembly 400 in which a braking surface of the brake rotor assembly 400includes three similarly shaped friction surface parts 204 and thestructural part 202 includes retaining ridges 402 or other similarstructures spaced such that each of the friction surface parts 204 canbe arranged on the receiving surface 206 of the structural part 202between two of the retaining ridges 402 when the brake rotor assembly400 is assembled. The retaining ridges 402 can provide rotationalstability such that the friction surface parts 204 are maintained in astationary relationship relative to the structural part 202. FIG. 5shows an assembled view 500 of the brake rotor assembly 400 shown inFIG. 4.

FIG. 6A, FIG. 6B, and FIG. 6C show views 600, 610, 620 of an additionalexample of a brake rotor assembly. In this example, the structural part202 includes a hub section 622 with sufficient bulk that a singlefriction surface part 204 that forms a complete circle would not bepossible to secure to at least one side of the structural part 202. In asimilar manner, tiling of two or more friction surface parts 204attached to a structural part 202 can allow accommodating of one or moreof slots, holes, grooves, or other features of the structural part 202.

The structural part 202 of a brake rotor assembly consistent withimplementations of the current subject matter can include one or morebulk materials, which can include, but are not limited to ceramics,metal matrix, composite materials, cast iron, carbon fiber, or the like.The friction surface parts 204 can be chosen from a variety of materialsas well. For example, in some implementations of the current subjectmatter, the friction surface parts 204 can be stainless steel. In thismanner, a stainless steel friction surface can be provided on a brakerotor assembly without requiring that the entire brake rotor assembly beformed of stainless steel. Given the expense of stainless steel, anapproach that allows a stainless steel braking surface without requiringthat an entire brake rotor assembly be formed of stainless steel can bequite beneficial.

In other implementations of the current subject matter, one or morefriction surface parts 204 forming part of a brake rotor assembly can beformed of a brake pad friction material. In such an arrangement, thefriction material 110 of a brake pad 106 of a braking system canoptionally include a same or different friction material. In the exampleof the brake pads 106 including the same fiction material as used on thefriction surface parts, the braking system can exhibit features ofadherent and/or adhesive friction, which can provide enhanced brakingpower relative to a conventional braking system. Alternatively, thebrake pads can be formed of some other material, such as for examplestainless steel, cast iron, a ceramic, a composite, or the like.

In still other implementations of the current subject matter, one ormore friction surface parts 204 can be coated with a wear and corrosionresistant coating. The brake pads in this example can include a frictionmaterial 110. Alternatively, the brake pads can include the wear andcorrosion resistant coating while one or more friction surface parts 204include a brake pad friction material. In these examples, the wear andcorrosion resistant coated parts (e.g. the brake pads 110 or thefriction surface parts 204) can include one or more levels of surfacetopography as discussed below. While the following description ofsurface topography levels refers to such features on friction surfaceparts 204 that are included in a brake rotor assembly, if will beunderstood that the same discussion can also apply to brake pad partshaving the wear and corrosion resistant coating and one or more levelsof surface topography.

Examples of surface topography can optionally include one or more scalesof surface topography, for example as illustrated in the diagram 700 ofa friction surface part 204 shown in of FIG. 7. At a first, largerscale, multiple island formations 702 can be included on a frictionsurface of the friction surface part 204. These multiple islandformations can form a regular or irregular pattern in which islands areseparated by channels 704, which can optionally have base surfaces 706that are roughened. In one example, a representative distance from a topsurface of the island formations 706 to a base surface 706 of channelsformed between the island formations 702 can be in a range ofapproximately 10 microns (0.0005 inches) to 3200 microns (0.125 inches).A ratio of the area occupied by the island formations to the areaoccupied by the channels 704 can optionally be in a range of one percentto ninety-nine percent or vice versa.

In some examples, at least part of the base surfaces 706 of theinter-island channels 704 can have a surface roughness sufficient tocreate turbulence to air masses flowing in a direction parallel to aplane defined by the friction surface 104 of the rotor assembly 200 towhich the friction surface part 204 is assembled, for example a surfaceorthogonal to an axis 112 about which the brake rotor assembly 200rotates with a wheel of a motor vehicle. It will be understood thatcross-sectional shapes of the island formations 702 can be substantiallyrectangular (e.g. as shown in FIG. 7) or any other regular or irregularshape. For example, the island formations 702 can have substantiallytriangular, substantially trapezoidal, substantially circular,substantially curved, or any other regular or irregular cross-sectionalshape as viewed in a plane perpendicular a friction surface 104 of abrake rotor 102. Various shapes of the island formations 702 as viewedin other planes are also within the scope of the current subject matter.For example, the island formations 702 can have substantially circular,substantially square, substantially rectangular, substantially tear dropshaped, substantially curved, or any other regular or irregular shape asviewed in a plane parallel to a friction surface 104 of the frictionsurface part 204.

A second, smaller scale of surface topography on a friction surface part204 can optionally include raised “peaks” 712 with spaced “valleys” 714between (and around, etc.) the peaks 712. A uniform pattern can be usedthroughout the friction surface part 204. Alternatively or in addition,a combination of different shaped surface features can be included topresent a visible design or texture that can vary in a random orpredetermined manner across the friction surface part 204. The peaks 712can optionally have sharp, angular cross-sectional shapes. Other shapesof the peaks 712 and valleys 714 are also within the scope of thisdisclosure. Shapes of the peaks 712 can include, but are not limited tosquares, trapezoids, rectangles, triangles, stars, letters or names,numbers, logos, trademarks, dashes, other geometric shapes, and thelike, with or without rounded corners. The shape and positioning of thepeaks 712 can be designed to be aesthetically pleasing in appearance,which is particularly desirable when the friction surface part 204 aspart of the brake rotor assembly 200 is externally visible, as is thecase with many motor cycle brake rotors and some automotive rotors usedin conjunction with alloy wheels or the like. The valleys 714 adjacentto and/or surrounding the peaks 712 can result in a significantreduction in the overall weight, which in turn can improve theefficiency and performance of the motor vehicle. Additionally, thevalleys 714 can allow for air flow around the peaks 712 for increasedcooling and heat dissipation. The base of each valley 714 can optionallybe roughened or modulated to provide bumps or the like that createturbulence in air flow along the valley 714 which can also improve thecooling effect.

Peaks 712 of desired shapes and dimensions can be formed in any suitablemanner, for example by appropriate machining or other forming processes.Such peaks and valleys or other “surface roughness” features can becreated on upper surfaces 710 of the island formations 702.

The second scale of surface topography can advantageously assist inretaining a transferred film or layer of brake pad material to thefriction surface part 204. In the example of FIG. 7, the upper surfaces710 of the island formations 702 can form the friction surface offriction surface part 204. The surface roughness at the second scale ofsurface topography (e.g. the peaks 712 and valleys 714) can act as anabrasive surface that effective scrapes some of the friction material110 from the opposed braking surface. For example, a brake pad material110 can be transferred onto a wear and corrosion resistant coatedfriction surface part 204 having one or more levels of surfacetopography as discussed above and being assembled as part of a brakerotor assembly, or brake pad material 110 can be transferred from afriction surface part 204 formed of such material onto a brake padhaving a wear and corrosion resistant coating and one or more levels ofsurface topography as discussed above. This transferred brake padmaterial can be retained on (or in, by, etc.) the surface topographyfeatures in a transfer film layer on the friction surfaces of the wearand corrosion resistant surface. This transfer film layer can beretained on the friction surface of the friction surface part 204 (orbrake pad having similar features) at least in part as a result of thesecond scale of surface topography, whose peaks 712 and valleys 714 canprovide a structure that resists easy wiping off or other dislodgingactions that might free the transfer film layer from a friction surfacepart 204 (or brake pad having similar features) that lacks suchfeatures.

The transfer film layer can provide significant benefits in bothdurability and braking effectiveness of the braking system 100. Forexample, the retained transfer film layer of the friction material canprotect the underlying material of the friction surface part 204 (orbrake pad having similar features) from abrasive friction interactionswith the friction material. Instead, the friction material can interactwith similar material present in the transfer film layer retained on thefriction surface part 204 (or brake pad having similar features). Thetransfer film can also act to seal one more surfaces of the frictionsurface part to provide at least partial protection from possiblecorrosion (e.g. by preventing contact of salt, water, minerals, etc.with the bare surface of the friction surface part 204). The presence ofsimilar materials on either side of the brake pad-brake rotorinteraction during actuation of a braking system 100 can also provideimprovements in braking power. In an example, the friction material andthe transfer film layer on the friction surface part 204 (or brake padhaving similar features) can experience a form of adherent and/oradhesive friction, in which brake pad material dynamically transfers ineither direction, for example back and forth between the frictionmaterial and the transfer film layer on the friction surface part 204(or brake pad having similar features), with a breaking and reforming ofmolecular bonds occurring as part of the process. This adherent and/oradhesive friction process can also be referred to as stiction.

While adherent and/or adhesive friction may occur to some small extentin previously available brake rotors, the absence of surface topographyfeatures (e.g. either or both of the peaks 712 and valleys 714 of thesecond scale of surface topography and optionally also the islandformation 702 and channels 704 of the first scale of surface topographydescribed herein) on the surfaces of conventional rotors can render thiseffect relatively insignificant. For example, the amount of transferredfriction material present per unit area in a transfer film layeroccurring on a conventional rotor can be orders of magnitude smallerthan that present in a friction surface part 204 (or brake pad havingsimilar features) having features described herein. Additionally,without a surface topography structure capable of retaining a transferfilm layer, the impact of adherent and/or adhesive friction can bediminished as the transfer film layer would not be laterally anchored tothe friction surface of the friction surface part 204 (or brake padhaving similar features) or otherwise resistant to rotational motionabout the friction surface of the friction surface part 204 (or brakepad having similar features) during actuation of the braking systemexcept by relatively weak van der Waals or electrostatic forces. Thefirst scale of surface topography (e.g. island formations 702 andchannels 704) and/or the second scale of surface topography (e.g. peaks712 and valleys 714) described herein, or functional or structuralequivalents thereof, can provide a mechanical anchoring mechanism bywhich a transfer film layer has increased resistance to rotationalforces and/or other forces or effects that might act to dislodge thetransfer film layer from the friction surface when the braking system100 is actuated. It should be noted that a transfer film layer can alsobe formed even without macro-scale surface topography features. Forexample, a polished surface of a friction surface part 204 (or brake padhaving similar features) having a wear and corrosion coating consistentwith those described herein can also retain a transfer film layer havingsimilar properties to those discussed above.

Other potential advantages can result for a friction surface part 204(or brake pad having similar features) having one or more scales ofsurface topography as described herein that are sufficient to generateand retain a transfer film layer that includes transferred frictionmaterial. For example, the transfer film layer can act as a protectivelayer that reduces abrasive friction on the friction surface of thefriction surface part 204 (or brake pad having similar features). Thisprotective feature can be beneficial in extending the useful lifetime ofa brake rotor assembly consistent with implementations of the currentsubject matter as overall wear of the friction surfaces can be reduced.Adherent and/or adhesive friction and/or one or more other mechanismsthat improve braking effectiveness of a braking system that includessuch a brake rotor assembly and with creation of a transfer film layercan also reduce wear of the friction material (e.g. from the brake pad106 or from a friction surface part 204 formed of the friction material.This effect may also result from the increased importance of adherentand/or adhesive friction relative to abrasive friction as well as thepossibility that a “stickier” brake rotor to brake pad materialinteraction can require less overall force to be applied duringactuation of the braking system. The presence of a transfer film layer,or possibly other factors or features of braking systems and methodsconsistent with the current disclosure, can also provide for a veryprogressive, linear braking feel, which can result in safer and morecontrollable braking. Decreased wear of the friction material of a brakepad can reduce an amount of friction material debris created duringactuation of the braking system 100 and released into the environment.As one or more chemical components of brake pad friction material can bedamaging to the environment, human health, etc., this effect can hassignificant advantages, particularly in view of increasing governmentalregulation of emission from braking systems.

A wear and corrosion resistant coating, either one that is consistentwith the examples described herein or one formed using other approaches,can cause surface topography features of a friction surface of afriction surface part 204 (or brake pad having similar features) to bepersistent and durable, even after prolonged use of the braking system(e.g. in operation of a motor vehicle or the like). Spacing of the peaks712 and valleys 714 that are formed in such a surface configuration canbe regular or irregular. The peak and valley configuration can operateduring braking to transfer some of the material of a brake pad to thebrake rotor such that subsequent braking can be enhanced due to adherentand/or adhesive friction between the similar brake pad material on thepad itself and on the rotor surface, as discussed in more detail below.

In implementations of the current subject matter, a friction surfacepart 204 (or brake pad having similar features) formed of stainlesssteel, cast iron, or some other bulk material having desirable bulkcharacteristics (e.g. sufficient rigidity, desirable weight properties,cost, etc.) can be prepared with a wear and corrosion resistant coating.Such a rotor can be cleaned, for example to remove impurities such asoil, grease, dirt, oxides, and the like.

The cleaned friction surface part 204 (or brake pad having similarfeatures) can then be pre-treated using a back-sputtering processperformed under a controlled atmosphere (e.g. a vacuum, a partialvacuum, an inert atmosphere such as argon, xenon, krypton, or the like,etc.). A back-sputtering process can include generating ions, which areaccelerated toward a surface of the brake rotor substrate by a biasingvoltage. In some examples, the biasing voltage can be in a range ofapproximately 800 to 1200 V or alternatively in a range of about 600 to1000 V, and the back-sputtering process can be applied for a duration ofabout 3 to 20 minutes or for other durations depending on one or more ofphysical properties of the friction surface part 204 (or brake padhaving similar features), desired surface characteristics, chemicalproperties of the friction surface part 204 (or brake pad having similarfeatures) material, etc. The pre-treatment process can further clean thesurface of the friction surface part 204 (or brake pad having similarfeatures) in addition to activating the surface to enhance itsreceptivity to subsequent physical vapor deposition processes.

One or more supporting layers of a preparatory metal or metal alloy canbe deposited onto surfaces of the pre-treated friction surface part 204(or brake pad having similar features). The one or more supportinglayers can act as a support for a wear and corrosion resistant outercoating applied to the friction surface part 204 (or brake pad havingsimilar features) consistent with the current subject matter. As usedherein, a preparatory metal or metal alloy can include one or more ofchrome, nickel, or other similar materials. The preparatory layer can beformed to meet a variety of functional or decorative purposes, such asfor example enhanced environmental corrosion protection, galvaniccorrosion protection (or perhaps to accelerate corrosion of asacrificial material or the like), regenerative braking,electro-magnetic braking, sensing, radio frequency identification(RFID), serving as decorative base layer for photo-chemical etching, orthe like. In optional variations, the material of a supporting layer canbe applied using a wet plating process, plasma spraying, or any othermethods capable of applying one or more metallic coatings with athickness in a range between a fraction of a micron to several thousandmicrons thick. In an advantageous implementation, the one or moresupporting layers of the preparatory metal can be applied using one ormore of a physical vapor deposition process, a sputtering process, anevaporative or cathodic arc process, or the like.

FIG. 8A shows a side cross-sectional view illustrating features of afriction surface part 204 (or brake pad having similar features) 800consistent with implementations of the current subject matter. A shownin FIG. 8A, an outer surface 801 of a friction surface part 204 (orbrake pad having similar features) has a supporting layer 804 applied toit. Subsequent to the coating of the friction surface part 204 (or brakepad having similar features) surface with the supporting layer 804, awear and corrosion resistant coating, which can include a first layer806 of a first layer material and a second layer 810 of a second layermaterial, can be applied over the supporting layer 804. In variousimplementations, the first layer material includes a metal or metalalloy, such as for example pure titanium metal or other metals (e.g.chromium, zirconium, aluminum, hafnium, etc.) and the second layermaterial includes a nitride, boride, carbide or oxide of the first layermaterial. Either or both of the first layer 806 and the second layer 810can be applied using a method such as physical vapor deposition,sputtering, or the like after the supporting layer 804 is in place. Eachof the first layer and the second layer can also be repeated, eitheralternatively (e.g. in a first layer, second layer, first layer, secondlayer sequence) or to build a larger amount of the first layer materialfollowed by a larger amount of the second layer material (e.g. in afirst layer, first layer, first layer, second layer, second layer,second layer sequence). In some implementations of the current subjectmatter as discussed below, one or more layers of graphene can beincluded, either as an additional layer or in some examples as areplacement for the first material and/or second material.

FIG. 8B shows a side cross-sectional view illustrating features of afriction surface part 204 (or brake pad having similar features)consistent with implementations of the current subject matter. As shownin FIG. 8B (and similar to the example of FIG. 8A, the outer surface 801of a friction surface part 204 (or brake pad having similar features)has a supporting layer 804 applied to it. Subsequent to the coating ofthe friction surface part 204 (or brake pad having similar features)surface with the supporting layer 804, a wear and corrosion resistantcoating, which can include a first layer 806 of a first layer materialand a second layer 810 of a second layer material, can be applied overthe supporting layer 804. FIG. 8B further illustrates that the depositedlayers need not be homogeneous and discrete. Instead, in one example, afirst layer 806 of the first material can be at least partiallyintegrated with a second layer 810 of the second material to form alayer 812 combining elements from each of the two layers.

A combination of the cleaning and pre-treating of the friction surfacepart 204 (or brake pad having similar features), in addition toapplication of a supporting layer 804, can provide a suitable substratefor subsequent deposition of one or more iterations of the first layer806 and second layer 810 of the wear and corrosion resistant coating asdiscussed elsewhere herein.

The first layer 806 can include an amorphous (non-crystalline) structureor a crystalline structure. The first layer 806 can include multiplelayers or multiple layers that can be merged to form a single layer. Thethickness of each layer of the first layer 806 can vary from one or afew atoms in depth to thousands of Angstroms. The surface irregularityor defect can be variations in the height of the parallel surfaces andangled surfaces between the variations in height illustrated in FIG. 7.In addition, the surface irregularity or modification can be formed aspeaks, valleys and angular surfaces between the peaks and valleys. Whenthe surface of the friction surface part 204 (or brake pad havingsimilar features) is subsequently coated with the supporting layer andthe wear and corrosion resistant coating, the coated surfaces cancontinue to exhibit a three dimensional appearance or surface texture.Furthermore, the surface texturing of the surfaces of the brake rotorare durable and wear resistant such that the three dimensionalappearance or surface texture persistent, even after extended use of abrake rotor that includes the friction surface part 204 (or brake padhaving similar features) in a vehicle braking system.

The wear and corrosion resistant coating can also include a second layer810 that overlays and contacts the first layer 806. Though the first andsecond layers 806, 810 and the supporting layer are depicted asdistinct, in some implementations of the current subject matter, thelayers intermingle or merge such that no distinct boundary existsbetween the layers. The second layer material can include one or morebinary metals, for example, one or more metal nitrides, metal borides,metal carbides and metal oxides. The second layer material can includeone or more nitrides, borides, carbides or oxides of the metal used inthe first layer. In some examples, amorphous titanium can form some orall of the first layer 806 and a titanium nitride (TiN, TiXN, etc.) canform all or some of the second layer 810. The multiple layers, forexample the first and second layers 806, 810, optionally repeated one ormore times, can be configured to form a lattice structure or a superlattice structure, which can include thin films formed by alternatelydepositing two different components to form layered structures.Multilayers become super-lattices when the period of the differentlayers is less than 100 angstroms. With this cooperation of structure, acoating having a service life to exceed approximately 100,000 vehiclemiles or more can be obtained. It should be noted that chemicalabbreviations (e.g. TiN, Ti2N, etc.) are used herein as a shorthandrather than an exact chemical label, and do not suggest that thestoichiometry of the indicated compound must be exactly as stated in theabbreviation.

The wear and corrosion resistant coating can cause surface roughnessfeatures on a surface of the friction surface part 204 (or brake padhaving similar features) to be significantly more durable to wear fromnormal braking activities. As such, peak 712 and valley 714 topography(or other surface topography features) that is originally present on thesurface of a friction surface part 204 (or brake pad having similarfeatures) prior to use in braking can persist for a large percentage ofthe useful life of the friction surface part 204 (or brake pad havingsimilar features), which can in some implementations be many multiplesof a typical useful lifetime for a conventional brake rotor without awear and corrosion resistant coating as described herein.

The hardness of the coating on the friction surfaces of a frictionsurface part 204 (or brake pad having similar features) can dictate howpersistent the surface roughness condition of the friction surfaces isover repeated braking events. A typical, uncoated brake rotorconstructed of stainless steel, light weight metal alloys (e.g. titaniumalloys), ceramic materials, ceramic composite materials, titanium, etc.and/or combinations thereof generally has a hardness as measured on theRockwell “C” scale of about 35±8. Cast iron, titanium, and otherrelatively softer materials can also be used in brake rotors. Thesurface roughness features of the surface of a friction surface part 204(or brake pad having similar features) according to implementations ofthe current subject matter can be characterized by an average amplitudebetween the peaks 712 and valleys 714 of the second scale of surfacetopography, which can in some implementations be in a range ofapproximately 0.6 μm to 0.85 μm (approximately 26-32 micro-inches). Inaddition to improved durability resulting from increased hardness of thesurface of a friction surface part 204 (or brake pad having similarfeatures), in some implementations of the current subject matter, acoating imparting wear and corrosion resistance consistent thedescriptions herein can also provide a type of solid lubrication. Forexample, inclusion of chromium and/or possibly other solidlubricant-type metals can cause the surface of the friction surface part204 (or brake pad having similar features) to be have increased hardnessas well as increased “slipperiness,” which can counteract the weareffects of abrasive friction occurring between a friction material of afriction surface of the friction surface part 204 (or brake pad havingsimilar features).

According to implementations of the current subject matter, an optimizedrelationship between the surface roughness and the surface hardness canbe obtained to maximize persistence of the peak 712 and valley 714surface roughness features over a useful lifetime of a brake rotorassembly or brake pad that includes a friction surface part 204 (orbrake pad having similar features). The optimal relationship between thesurface roughness and surface hardness is one at which the peak andvalley topography is maintained to allow continued transfer andretention of friction material to a friction surface of the frictionsurface part 204 (or brake pad having similar features) such thatadherent and/or adhesive friction between the transferred frictionmaterial and the friction material adds to abrasive friction forcesbetween the friction surface part 204 (or brake pad having similarfeatures) and the friction material to improve the stopping power of abraking system 100.

Excessive hardness may lead to brittleness, while too little hardnessmay lead to premature wear of the surface roughness features. Also,excessive surface roughness may lead to too rapid a consumption of thefriction material as too much of the friction material is transferred toand potentially scaled away from the friction surface of the frictionsurface part 204 (or brake pad having similar features). Too littlesurface roughness on the friction surface part 204 (or brake pad havingsimilar features) may lead to too little transfer of friction materialand/or too little retention of the transferred friction material on thefriction surfaces of the friction surface part 204 (or brake pad havingsimilar features), thereby weakening the braking power and potentiallyrequiring greater reliance on abrasive friction, which can lead toincreased wear.

An additional variable in the analysis of an optimal surface roughnessand surface hardness regime can be the composition and other physicalproperties of the friction material. For example, a brake pad material(e.g. a friction material) that is readily transferrable and/oradherable to a friction surface of a friction surface part 204 (or brakepad having similar features) may require a less pronounced surfaceroughness to create the advantages disclosed herein for the inventivesubject matter. In such an example, a relatively lower surface roughnessmay be used in conjunction with an increased surface hardness as thelower amplitude between the peaks 712 and valleys 714 of the surfacetopography of the friction surface part 204 (or brake pad having similarfeatures) can be less prone to damage due to the increased brittlenessthat can accompany increased surface hardness.

In addition to the implementations of the current subject matterdiscussed above, other configurations are also contemplated. Forexample, a brake rotor assembly that includes multiple friction surfaceparts 204 need not have all of the friction surface parts 204 includeidentical friction surfaces. In this manner, some of the frictionsurface parts 204 can be optimized for one braking condition while otherof the friction surface parts 204 can be optimized for other brakingconditions.

FIG. 9 shows a process flow chart 900 illustrating features that can bepresent in one or more implementations of the current subject matter. At905, a friction surface part having a contact surface is positioned on areceiving surface of a structural part. The contact surface is alignedperpendicularly to an axis of rotation of the structural part. At 910,the friction surface part is fixably attached to the receiving surfaceof the structural part such that the contact surface faces away from thereceiving surface of the structural part to form at least part of anannular braking surface arranged concentrically around an axis ofrotation of the structural part.

In the descriptions above and in the claims, phrases such as “at leastone of” or “one or more of” may occur followed by a conjunctive list ofelements or features. The term “and/or” may also occur in a list of twoor more elements or features. Unless otherwise implicitly or explicitlycontradicted by the context in which it used, such a phrase is intendedto mean any of the listed elements or features individually or any ofthe recited elements or features in combination with any of the otherrecited elements or features. For example, the phrases “at least one ofA and B;” “one or more of A and B;” and “A and/or B” are each intendedto mean “A alone, B alone, or A and B together.” A similarinterpretation is also intended for lists including three or more items.For example, the phrases “at least one of A, B, and C;” “one or more ofA, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, Balone, C alone, A and B together, A and C together, B and C together, orA and B and C together.” Use of the term “based on,” above and in theclaims is intended to mean, “based at least in part on,” such that anunrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems,apparatus, methods, and/or articles depending on the desiredconfiguration. The implementations set forth in the foregoingdescription do not represent all implementations consistent with thesubject matter described herein. Instead, they are merely some examplesconsistent with aspects related to the described subject matter.Although a few variations have been described in detail above, othermodifications or additions are possible. In particular, further featuresand/or variations can be provided in addition to those set forth herein.For example, the implementations described above can be directed tovarious combinations and subcombinations of the disclosed featuresand/or combinations and subcombinations of several further featuresdisclosed above. In addition, the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. Other implementations may be within the scope of the followingclaims.

1. A brake rotor assembly, comprising: a structural part having areceiving surface aligned perpendicularly to an axis of rotation of thestructural part; a friction surface part having a contact surface, thefriction surface part fixably attached to the receiving surface of thestructural part such that the contact surface faces away from thereceiving surface of the structural surface to form at least part of anannular braking surface arranged concentrically around the axis ofrotation.
 2. A braking system comprising: the brake rotor assembly ofclaim 1; a brake pad comprising a friction material; and an apparatusfor urging the friction material of the brake pad against the annularbraking surface to slow rotation of the brake rotor assembly and avehicle axle to which the brake rotor assembly is rotationally fixed. 3.A braking system as in claim 2, wherein the friction material comprisesat least one of stainless steel, cast iron, a ceramic, and a composite,and the friction surface part comprises a brake pad material.
 4. Abraking system as in claim 2, wherein the friction material of the brakepad comprises at least one of stainless steel, cast iron, a ceramic, acomposite, and a brake pad material.
 5. A braking system as in claim 2,wherein the friction material of the brake pad comprises a wear andcorrosion resistant coating.
 6. A braking system as in claim 2, whereinthe contact surface of the friction surface part comprises a samematerial as the friction material of the brake pad.
 7. A braking systemas in claim 2, wherein the friction material of the brake pad comprisesone or more levels of surface topography
 8. A brake rotor assembly as inclaim 1, wherein the friction surface part comprises a plurality offriction surface parts arranged on the receiving surface to form the atleast part of the annular braking surface.
 9. A brake rotor assembly asin claim 1, wherein the friction surface part comprises at least one ofstainless steel, cast iron, a ceramic, a composite, and a brake padmaterial.
 10. A brake rotor assembly as in claim 1, wherein the contactsurface of the friction surface part comprises a wear and corrosionresistant coating.
 11. A brake rotor assembly as in claim 10, whereinthe contact surface of the friction surface part comprises one or morelevels of surface topography.
 12. A brake rotor assembly as in claim 11,wherein the one or more levels of surface topography comprise a firstlevel comprising island formations separated by channels.
 13. A brakerotor assembly as in claim 11, wherein the one or more levels of surfacetopography further comprise a second level comprising raised peaks withspaced valleys between the peaks.
 14. A brake rotor assembly as in claim13, wherein the second level of surface topography assists in retainingthe transferred film or layer of brake pad material on the contactsurface.
 15. A brake rotor assembly as in claim 14, wherein thetransferred film or layer of brake pad material enhances braking byparticipating in adhesive friction with a brake pad.
 16. A brake rotorassembly as in claim 1, wherein the structural part is formed of atleast one bulk material selected from a ceramic, a metal matrix, acomposite material, cast iron, and carbon fiber.
 17. A brake rotorassembly as in claim 1, wherein the structural part comprises a physicalstructure to enhance cooling.
 18. A brake rotor as in claim 17, whereinthe physical structure comprises a vane and/or a channel.
 19. A brakerotor assembly as in claim 1, further comprising an attachment featurefor fixably attaching the friction surface part to the receivingsurface.
 20. A brake rotor as in claim 19, wherein the attachmentfeature comprises at least one of a screw, a bolt, a connecting pin, anadhesive, a weld, a braze, a retaining ridge and, an at least partiallyrecessed or indented area on the receiving surface into which at leastpart of the friction surface part is seated.
 21. A method for assemblinga brake rotor assembly, the method comprising: positioning a frictionsurface part having a contact surface on a receiving surface of astructural part; fixably attaching the friction surface part to thereceiving surface of the structural part such that the contact surfacefaces away from the receiving surface of the structural part to form atleast part of an annular braking surface arranged concentrically aroundan axis of rotation of the structural part.